Missing methane emissions from leaves of terrestrial plants

The controversial claim that attached leaves of terrestrial plants emit CH4 aerobically remains to be corroborated. Here, we report CH4 fluxes and CO2 exchange rates for leaves of the C-4 species Zea mays using a high-accuracy traceable online analytical system. In contrast to earlier results for Z. mays, our measurements provide no evidence for substantial aerobic CH4 emissions from photosynthesizing leaves illuminated with photosynthetically active radiation (lambda=400-700 nm), or from dark-respiring leaves. Preliminary measurements with the same system indicated a similar lack of aerobic CH4 emissions in the light or dark from leaves of the C-3 species Nicotiana tabacum. These findings are supported by independent high-precision C-13-labeling studies that also failed to confirm substantial aerobic CH4 emissions from plants. Nevertheless, we are not able to exclude the possibility that CH4 emissions from plants may be linked to nonenzymatic processes with an action spectrum lying outside the wavelength range for photosynthesis.